README.md: comment out Bintray references [ci skip]
README.md: comment out Bintray references [ci skip]

The goal is to avoid confusion by offering two separate download
endpoint for no real benefit. Though the Bintray site can be
used to pick older versions for testing.

Closes https://github.com/curl/curl-for-win/issues/11

vszakats/harbour-deps,vszakats/harbour-deps